1. Technical Field
The present invention relates to a laminate composite comprising a main body, a porous layer disposed on the main body and a further material which is or comprises a plastic and is adhesively bonded to the porous layer. Furthermore, the present invention relates to a use of fluorothermoplasts for binding the further material to the porous layer along with a process for producing a laminate composite.
2. Related Art
In particular, these laminate composites are used as bearing materials for plain bearings. The laminate composites generally have a main body onto which a porous layer (usually metallic) is applied. This is then impregnated with and enclosed by a further material. This further material is typically a plastic. There are two main types of plastics that can be used here: PTFE-based plastics and materials which can be processed using thermoplastics.
Depending on the use, the laminate composites can be used in plain bearings for non-lubricated, initially lubricated or media-lubricated applications. Initially lubricated plain bearings are lubricated once during installation, for example using grease. The materials used behave differently in these methods of application. In addition to the compatibility of the corresponding laminate composite with the lubricant, other important material properties for media-lubricated use are its resistance to erosion, delamination and wear.
Flow conditions can arise in the cracked bearing. These corrode the laminate composite or can lead to penetration of the lubricant in the laminate composite, resulting in the layers being separated from one another. The friction which occurs in connection with the lubricant is also important. This is because, for example, friction affects response behaviour when used for guide bushings in shock absorbers or it will affect efficiency when used in pumps.
The properties of the further material used in the media-lubricated bearings can be characterised as follows: Using thermoplastic matrix plastics leads to increased strength and an associated improvement in the anchoring in the porous layer, therefore almost no mechanical damage related to the flow conditions is caused. However, the friction from thermoplastic matrix plastics in connection with media is clearly higher than in PTFE-based materials. The latter are typically distinguished by a particularly low friction coefficient for media lubrication, whilst their flow resistance is limited due to the weak PTFE matrix. Furthermore, unlike thermoplastics, the anchoring of the further PTFE-based material in the porous layer is not supported by any adhesive forces.
Laminate composites which comprise a further PTFE-based material have been used in media-lubricated applications with higher flow loads for several years now. The PTFE base of the further material is modified using MoS2 as a solid lubricant. This type of laminate composite is used, for example, in shock absorbers. Here, it is necessary to achieve response behaviour which has the lowest amount of friction possible due to the requirements for ride comfort.
This type of laminate composite, however, has limited resistance when used in non-lubricated or dry and media-lubricated applications. Special laminate composites based on PTFE which are optimised for wear have therefore been developed for the media-lubricated applications, such as those outlined in DE 196 14 105 B4. An increased resistance to wear and tear is achieved through the addition of iron oxide; however there is a slight increase in the amount of friction depending on the conditions of use.
DE 198 08 541 C1 describes the improvement to the wear of the lubricant layer achieved by adding powdered polyaramids to PTFE, however this does not result in an improved flow resistance. Fluorothermoplasts PFA, FEP, ETFE, PVDF, PCTFE are often mixed in with the material for this purpose, for example as described in DE 33 43 697 A1. Owing to the chemical structure, these have a positive influence on the resistance of the material as they are more tightly bound to the PTFE in the lubricant layer, they allow additives to bind more effectively and they improve the adhesion of the substrate since the fluorothermoplasts reduce the anti-adhesive property of the PTFE. However, the more these properties are sought, the more fluorothermoplast must be added; the consequence of which is indeed an increased friction coefficient.
WO99/05425 describes the production of a laminate composite with a PTFE-based lubricant layer, wherein a PTFE-based film is affixed onto a metal substrate using a fluorothermoplast film. This structure is not however suitable for porous substrates and the associated production method using a PTFE paste. The PTFE mix cannot be impregnated into the pores of the porous layer in the form of an aqueous paste, for example as described in DE 195 07 045 C2, because an intermediate film prevents impregnation by rolling in and the film cannot be repositioned in the rolling process.